5aPAb11. Experimental investigation of onset threshold for shape
oscillations for air bubbles in 1g.

Experimental observations of single bubble oscillations have yielded a wide
variety of phenomena: periodic and period-doubled spherical oscillations;
periodic, quasiperiodic and chaotic multimode shape oscillations; and, most
recently, periodic, period-doubled, quasiperiodic, and chaotic sonoluminescence.
In an effort to determine the effect of gravity on these phenomena, the acoustic
pressure threshold for shape oscillations of single gas bubbles in a 1g
environment was measured. The bubble sizes varied between 20 and 100 5-m radius,
and were simultaneously levitated and driven acoustically at 20 kHz in water.
Mie scattering was used to measure the bubble radius and to monitor its motion
before and after the onset of surface instabilities giving rise to shape
oscillations. A video imaging system was used to determine the mode of the shape
oscillations. [Work supported by NASA.]